Thoughts on Change and Defaults

Observations:

• Different facts have different rates of change Example (fast to slow):

  • Current time
  • Current location
  • Daily weather
  • Current GPA
  • Current president

• How can system know that some pieces of information change temporally and some change retroactively Example:

  • If someone dies, information about whether they are alive or not has undergone temporal change. The idea that that they are dead is only true after they have died, and not before that event.
  • If the system thinks all birds can fly and then learns of penguins, the information (all birds can fly) changes to (most birds can fly)
    • The system may want to know that it believed (all birds can fly) before this change, but it must know that (most birds can fly) is now true at all times and not just after the event that changed this idea.

• A reasoning system should be flexible enough to accomodate facts that change quickly (time/location)

• Should not reach a contradiction because current value is different from a previous value in those cases

• Could be unreasonable to store data in a temporal fashion

• Note that this concept is similar to defaults
  Example: Perhaps the system lives in an arid region

  • Slow changing information: The weather is usually dry
  • Fast changing information: Today's humidity is 25%
    If the system is asked what is the weather going to be tommorow the response will use the fact that the area is usually dry -> humidity will be ~25%
    Daily humidity may be different and change frequently, but the fact that the region is arid which causes low humidity will rarely change.